1. Field of the Invention
This invention relates to a method of and a system for monitoring during operation the conditions of a journal bearing having a bearing surface for supporting a rotary shaft through an oil film.
2. Description of the Prior Art
A journal bearing is used for supporting a rotor of a rotary machine, such as a steam turbine, a generator, etc. For the journal bearing used for this purpose, a suitable type of journal bearings are selected that have a diameter and width considered optimum in view of the weight of the rotor, the torque transmitted by the rotor, and other factors.
A rotor of a large type rotary machine weight over 200 tons and is usually rotated at a high speed in the range between 1500 and 3600 rpm, so that the bearing for supporting the shaft of the rotor are required to be built solidly and continue to operate in normal conditions during operation. The shaft and the bearing surface are displaced relative to one another due to various factors. As a result, a load applied to the bearing might inordinately increase or decrease to cause the thickness of the oil films to be abnormally decreased or increased, respectively. An increase in the thickness of an oil film of a bearing might subject the rotor to abnormal vibration such as steam whirl, thereby developing a rubbing between the rotor and a stator. A decrease in the thickness of an oil film of a bearing might render the oil film discontinuous and raise the temperature of the surface layer of the bearing, thereby causing seizure to occur on the surface layer of the bearing.
Relative displacements of a shaft and a bearing surface would be mainly caused by the fact that thermal deformation of a support for a bearing under the influences of ambient temperature causes the bearing to be vertically displaced or causes the bearing to be inclined with respect to the bearing surface, the fact that a variation in the internal pressure of a turbine casing causes a bearing support to be vertically displaced or inclined with respect to the shaft when the rotary machine is a turbine, and the fact that a plurality of portions of amount supporting the rotary machine are non-uniformly depressed with time.
In view of the foregoing, it will be understood that it is possible to accurately grasp the conditions of a bearing by determining the load on the bearing during operation.
Heretofore, proposals have been made to continuously monitor and measure the temperature of oil fed to a bearing and discharged therefrom, the pressure of the oil fed to the bearing, and the temperature of the surface layer of the bearing, to determine the conditions of the bearing. The temperature of the oil fed to and discharged from a bearing is insensitive to changes in the load on the bearing, so that it is very difficult to judge the bearing load merely based on the temperature of the oil. The pressure of the oil fed to the bearing has nothing to do with the load on the bearing. It is impossible to obtain the bearing load merely based on the temperature of the surface layer of the bearing.
U.S. Pat. No. 4,118,933 to Coleman et al. discloses an arrangement in which strain gauges are mounted on a bearing support structure for measuring the bearing load. This arrangement, however, is not intended to obtain the bearing load based on the pressure of an oil film between the bearing surface and the shaft.